Fatty acid esters of saccharide are very useful compounds such that they are finding their wide applications such as additives for food, cosmetics, drugs, resins, etc., detergents for clothing, detergents for the kitchen, shampoos, and the like as a surface-active agent which can fundamentally solve such problems as environmental pollution, toxicity for living organisms, and the like because of their high biodegradability and safety.
The preferred processes for preparing fatty acid esters of saccharide among those known in the art include one according to alcoholysis of saccharide with fatty acid lower alkyl esters, and one according to alcoholysis of saccharide with fats and fatty acids, that is, fatty acid triglyceride.
Especially, the latter process has great advantages as a process for preparing fatty acid esters of saccharide, because the process generally makes it possible to directly use relatively cheap animal and plant fats and oils such as beef tallow, palm oil, coconut oil and the like as starting material. The reaction product obtained by the above process contains fatty acid glycerides, which are usually a mixture of unreacted fatty acid triglyceride, fatty acid diglyceride and fatty acid monoglyceride, soap, and unreacted free saccharide besides fatty acid esters of saccharide, and these impurities are required to be removed therefrom in order to purify the fatty acid esters of saccharide.
Among these impurities, the soap and free saccharide can be almost completely removed easily and without substantial loss of fatty acid esters of saccharide according to a process by the application of the conversion to their derivatives, difference in their solubilities in solvent, or the like.
On the other hand, according to a method known in the art for removing fatty acid glycerides, a solid-liquid extraction is effected by the use of an organic solvent such as acetic esters, ketones, and the like to remove the fatty acid glycerides. Difference in solubility in an organic solvent between fatty acid esters of saccharide, especially fatty acid polyesters of saccharide having two or more ester linkages in one molecule and fatty acid glycerides is so small that it is extremely difficult for the former to be separated completely from the latter. Therefore, the conventional methods mentioned above have such serious defects that the complete removal of fatty acid glycerides causes a high loss of fatty acid esters of saccharide.
Accordingly, it is an object of the present invention to provide a novel method for purifying fatty acid esters of saccharide in order to overcome the above defects due to the conventional processes.